Root absorption of 14C-5 (ring)-metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] from hydroponic culture and its subsequent translocation in tolerant (‘Russet Burbank’) and susceptible (‘Chipbelle’) potato (Solanum tuberosum L.) cultivars were measured. Differences in root absorption did not appear to be as important to differential tolerance as did translocation differences. Total available metribuzin absorbed was 6 and 7%, 18 and 29%, and 31 and 45% after 1, 4, and 8 days for Russet Burbank and Chipbelle, respectively. Radioactivity was concentrated in stems, petioles, and leaf veins in the tolerant cultivar, whereas interveinal leaf tissue was the major accumulation site for 14C in the susceptible cultivar. Of the total radioactivity in the plants after 8 days, 82 and 87% were in the foliage for the tolerant and the susceptible cultivar, respectively. Translocation was apoplastic. Metribuzin tolerance by Russet Burbank is due in part to restricted translocation to the leaf blades. A model for differential transport between cultivars is proposed.

Rust-specific polymerase chain reaction (PCR) primers selectively amplified ribosomal DNA of a rust fungus from infected dyers woad. PCR enabled DNA of the fungus to be detected in symptomatic plants as well as in asymptomatic parts of diseased plants. The use of PCR enabled early detection of rust infections in dyers woad plants during their first season when they are often asymptomatic Dried plant samples stored at room temperature for several months worked as well as lyophilized material for DNA extraction prior to PCR. The PCR detection method should greatly facilitate further studies on the biology and inoculation of this and other systemic rusts that have potential for use in biocontrol of weeds.

Sheep sorrel is an invasive, creeping perennial weed of lowbush blueberry fields. It is one of the most prominent weeds in blueberry fields in Nova Scotia and is responsible for decreasing yields. Three levels of fertilizer (0, 20, 40 kg N ha−1) and two levels of hexazinone (0 or 1.92 kg ai ha−1) were applied to experimental plots to determine their effects on sheep sorrel density. Sprout-year hexazinone reduced sheep sorrel densities, which led to increased yields. Fertilizer increased weed density in the absence of herbicides, had no effect on density in the presence of herbicides, tended to have no impact on floral buds, and did not increase yields. Fruiting-year hexazinone decreased sheep sorrel densities in some situations, but did not result in yield increases.

Ten years of Oregon Seed Certification Service (OSCS) preharvest field inspections converted from a nonspatial database to a geographic information system (GIS) were analyzed for patterns in spatial distribution of occurrence and severity of the 36 most common weeds of grass seed crops. This was done under the assumptions that those patterns would be primarily consequences of interactions among farming practices, soil properties, and biological traits of the weeds, and that improved understanding of the interactions would benefit the grass seed industry. Kriging, Ripley's K-function, and both Moran's I spatial autocorrelation and Getis-Ord General G high/low clustering using the multiple fixed distance band option all produced roughly similar classifications of weeds possessing strongest and weakest spatial clustering patterns. When Moran's I and General G analyses of maximum weed severity observed within individual fields over the life of stands were conducted using the inverse distance weighting option, however, results were highly sensitive to the presence of a small number of overlapping fields in the 10-yr record. Addition of any offset in the range from 6 to 6,437 m to measured distances between field centroids in inverse distance weighting matrices removed this sensitivity, and produced results closely matching those for the multiple fixed distance band method. Clustering was significant for maximum severity within fields over the 10-yr period for all 43 weeds and in 78% of single-year analyses. The remaining 22% of single-year cases showed random rather than dispersed distribution patterns. In decreasing order, weeds with strongest inverse-distance spatial autocorrelation were German velvetgrass, field bindweed, roughstalk bluegrass, annual bluegrass, orchardgrass, common velvetgrass, Italian ryegrass, Agrostis spp., and perennial ryegrass. Of these nine weeds, distance for peak spatial autocorrelation ranged from 2 km for Agrostis spp. to 34 km for common velvetgrass. Weeds with stronger spatial autocorrelation had greater range between distance of peak spatial autocorrelation and maximum range of significance. Z-scores for General G high/low clustering were substantially lower than corresponding values for Moran's I spatial autocorrelation, although the same two weeds (German velvetgrass and field bindweed) showed strongest clustering using both measures. Simultaneous patterns in Moran's I and General G implied that management practices relatively ineffective in controlling weeds usually played a greater role in causing weeds to cluster than highly effective practices, although both types of practices impacted Italian ryegrass distribution. Distance of peak high/low clustering among perennial weeds was smallest (1 to 3 km) for Canada thistle, field bindweed, Agrostis spp., and western wildcucumber, likely indicating that these weeds occurred in patchy infestations extending across neighboring fields. Although both wild carrot and field bindweed doubled in average severity over the period from 1994 to 2003, wild carrot was the only weed clearly undergoing an increase in spatial autocorrelation. Soil chemical and physical properties and dummy variables for soil type and crop explained small but significant portions of total variance in redundancy and canonical correspondence analysis of weed occurrence and severity. Fitch-Morgoliash tree diagrams and Redundancy Analysis (RDA) and Canonical Correspondence Analysis (CCA) ordinations revealed substantial differences among soil types in weed occurrence and severity. Gi∗ local hot-spot clustering combined with feature class to raster conversion protected grower expectations of confidentiality while describing dominant spatial features of weed distribution patterns in maps released to the public.

Greenhouse replacement-series experiments were conducted to evaluate the competitiveness of cowpea, sunn hemp, and velvetbean when grown in combination with yellow nutsedge and smooth pigweed. The effect of the cover crop species on yellow nutsedge tuber production was also evaluated. Cowpea and velvetbean were equally competitive with yellow nutsedge, but sunn hemp was less competitive. Although sunn hemp height was double that of cowpea or velvetbean, photosynthetically active radiation penetrating to the soil surface was twofold to eightfold greater than with the other two species. Leaf area per plant with sunn hemp monocultures were only 63 to 70% of cowpea and 37 to 41% of velvetbean. Increasing the proportion of cover crops in crop : weed mixtures did not significantly affect nutsedge tuber number per plant or tuber weight per plant. Cowpea was more competitive than smooth pigweed, whereas both sunn hemp and velvetbean were less competitive than smooth pigweed. The utility and efficacy of leguminous cover crop species for nutsedge and smooth pigweed suppression do not appear to be due to inherent competitiveness. Until cultivars that are more competitive become available, cultural measures should be employed that enhance cover crop modification of soil environmental conditions to minimize weed seed germination and vegetative propagule sprouting.

The antidote R-25788 (N,N-diallyl-2,2-dichloroacetamide) protected corn (Zea mays L. ‘DeKalb 315A’) seedlings from injury caused by the acetanilide herbicides, alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide], metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], H-22234 [N-chloroacetyl-N-(2,6-diethylphenyl)glycine ethyl ester], and H-26910 [N-chloroacetyl-N-(2-methyl-6-ethylphenyl)glycine isopropyl ester] in a greenhouse study. R-25788, however, did not protect four weed species tested. R-25788 only partially protected corn from injury caused by acetochlor [2-chloro-N-(ethoxymethyl)-6′-ethyl-o-acetotoluidide]. R-25788 was an effective antidote whether applied preemergence, preplant-incorporated, or as a tank mix. Injury symptoms caused by EPTC (S-ethyl dipropylthiocarbamate) and the acetanilide herbicides were similar; both caused leaf twisting and rolling, and at high rates leaves failed to emerge through the coleoptile.

In greenhouse studies, Cyperus esculentus L. var. esculentus was less susceptible than C. esculentus L. var. leptostachyus Boeck. to preplant applications of 1.77 kg/ha of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] or 0.5 kg/ha of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5-(4H)one]. C. var. esculentus was more susceptible than C. var. leptostachyus to postemergence applications of 2,4-D [(2,4-dichlorophenoxy)acetic acid] oil-soluble amine. C. var. esculentus had longer, slightly narrower, and more upright leaves; generally fewer but larger tubers; fewer rhizomes; and a lower frequency of flowers with less seeds per inflorescence than C. var. leptostachyus. Publications on C. esculentus should specify which variety was used.

In a 3 year herbicide-crop rotation involving corn (Zea mays L. ‘Coker 811A’), cotton (Gossypium hirsutum L. ‘Carolina Queen’), and peanuts (Arachis hypogaea L. ‘Argentine’), uncontrolled yellow nutsedge (Cyperus esculentus L.) and annual weeds drastically reduced all crop yields. By the end of the rotation sequences, intensive cultivation throughout the rotation killed 97 to 99% of the nutsedge tubers, but this level of control depended on hand-weeding the cotton. Moderate application of herbicides killed from 78 to over 99% of the yellow nutsedge tubers, while intensive treatment with herbicides produced at least 99% kill. In addition, all annual weeds present when the experiment was initiated were controlled satisfactorily by intensive herbicide applications except Florida beggarweed [Desmodium tortuosum (Sw.) DC.] in peanuts. The major change in composition of the weed population was a reduction in yellow nutsedge and in the total number of weeds; however, certain other population shifts also seemed affected by the weed control treatments. Compared to intensive cultivation, the investment in intensive herbicide treatment produced maximum yields and highest gross profit per acre. None of the treatments affected the market grade or organoleptic characteristics of peanuts. The fatty acid content of corn and cotton changed significantly only in 1967.

Field studies were conducted to determine the effects of various barnyardgrass populations on growth, yield, and nutrient concentration of transplanted “Jetstar’ tomato. Barnyardgrass densities at 16, 32, and 64 plants/m tomato row were tested in 1982 and 1983. Barnyardgrass shoot fresh weights/unit area increased as density increased. Fresh weight of barnyardgrass shoots ranged from 17 100 kg/ha at 16 plants/m of row to 35 500 kg/ha at 64 plants/m of row. At the vegetative stage, tomato shoot dry weight was unaffected by barnyardgrass. As crop growth progressed, tomato shoot dry weight decreased at all barnyardgrass densities. Season-long interference of barnyardgrass reduced marketable tomato fruit number and fruit weight at all densities compared to weed-free plots. Reductions in marketable fruit weight ranged from 26% to 16 plants/m row to 84% at 64 plants/m row. In 1982, concentrations of N, P, K, Ca, and Mg in tomato shoots were unaffected by season-long interference of barnyardgrass at all densities. However, in 1983, concentrations of N and K decreased and concentration of P increased in tomato leaves as the density of barnyardgrass increased. Concentrations of Ca and Mg in tomato leaves were unaltered by barnyardgrass density.

The relative activities of (R) and (S) enantiomers of the methyl ester of haloxyfop were determined on annual grasses. Samples enriched in the (S) enantiomer were markedly less active than the (R) in petri dish evaluations and foliar applications. The pure (S) enantiomer was estimated by regression to be 1000-fold or less active than the (R). The activity of the (S) enantiomer was found to be equivalent to that of the (R) following preemergence applications. Isolation and characterization of haloxyfop from soil treated with the methyl ester of haloxyfop indicated inversion of the (S) enantiomer to the (R) enantiomer within 7 days. Field trials confirmed the differential activity of enantiomers applied postemergence and their equivalence when applied preemergence. These findings indicate that inversion of the (S) enantiomer to the (R) occurs in soil following preemergence applications.

Ethylene gas stimulated seed germination of the pearl millet [Pennisetum americanum (L.) K. Schum] strain of Striga hermonthica (Del.) Benth. # STRHE) in two soil types in the North Kordofan Region of Sudan. Soils were the noncracking clay pediplain or ‘Gardud’, in Arabic, and the stabilized sand locally called ‘Qoz’. Ethylene at 1.5 kg ai/ha induced greater seed germination (suicidal seed germination) in the Gardud soil than in the Qoz soil. However, ethylene at 3.0 kg ai/ha was better on Qoz than Gardud soil. The effect of injection depth of ethylene was dependent on soil type. Ethylene was more effective when injected at a 15-cm depth in the Gardud soil and at a 30-cm depth in the Qoz soil. The viable population of S. hermonthica seed was reduced by suicidal seed germination at soil depth to 60 cm and to a horizontal distance of 25 cm from the point of ethylene injection. Ethylene-induced germination reduced seed population by 67 and 34% in Gardud and Qoz soils, respectively. A single injection of ethylene diffused up to 300 cm horizontally and up to 60 cm vertically and caused 12.6 and 8.5% reduction in viable 5. hermonthica seed in Gardud and Qoz soils, respectively. The potential of ethylene gas as an effective tool in striga control operations in a pediplain and stabilized sand soil such as is found in N. Kordofan is dependent upon the availability of the gas and the injection apparatus and the economics of its application.

Field experiments were conducted in Princeton, KY, in 1982, 1983, and 1984 to evaluate johnsongrass [Sorghum halepense (L.) Pers. # SORHA] control programs in no-tillage, doublecropped soybeans [Glycine max (L.) Merr. ‘Essex′]. Sequential applications of sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} or fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} at 0.2 kg ai/ha provided 36 to 94% johnsongrass control. The lower control values from these treatments were obtained in the droughty 1983 growing season while the higher and acceptable control ratings were obtained in 1982 and 1984 when rainfall was more plentiful. Preplant applications that contained glyphosate [N-(phosphonomethyl)glycine] provided johnsongrass control greater than those containing paraquat (1,1′-dimethyl-4,4′-bypyridinium ion). Soybean yields and soil moisture were greater with preplant applications of glyphosate than with preplant applications of paraquat or foliar applications of sethoxydim, fluazifop, or glyphosate. Greatest yields were obtained with a combination of a preplant application of glyphosate and a postemergence application of sethoxydim.

Twenty-nine wild oat (Avena fatua L. ♯3 AVEFA) and Avena sterilis L. ♯ AVEST accessions having various areas of origin and/or growth characteristics were grown to maturity in controlled environmental chambers. The four environments consisted of a 16-h photoperiod until 3 weeks after emergence, when the photoperiod was decreased (DP) 1 h per week for 8 weeks at a constant 14, 20, or 26 C (DP 14, DP 20, or DP 26); and an 8-h photoperiod until 3 weeks after emergence, when the photoperiod was increased (IP) 1 h per week for 8 weeks at a constant 20 C (IP 20). The relative growth rate of the accessions was similar in each environment. The length of the second leaf was up to 15 cm greater under 8- than 16-h day length at 20 C for some accessions, but was similar under both day lengths for other accessions. The width of the second leaf was greater under 14 than 20 C and was narrower with a 16-h than an 8-h photoperiod. Tiller initiation was slower in the DP 14 and IP 20 than in the DP 20 and DP 26 environments. Days to panicle emergence for individual accessions ranged from 10 to 57 days higher in the DP 14 than in the DP 20 environment. Seed produced on plants grown at 14 C had lower germination in water and 1500 ppm gibberellic acid than seed from plants grown at 20 C. Wild oat accessions varied in morphological characteristics, days to panicle emergence, and dormancy, and responded differently to changes in photoperiod and temperature. Wild oat morphological characteristics, days to panicle emergence, and dormancy did not consistently relate to species or area of origin.

The initial and residual toxicities, after 13, 22, and 31 weeks, of dimethyl 2,3,5,6-tetrachloroterephthalate (DCPA), 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), 3-(hexahydro-4,7-methanoindan-5-yl)-1,1-dimethylurea (norea), 2,4-bis(isopropylamino)-6-methylmercapto-s-triazine (prometryne), and α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) were determined in the greenhouse in four soil types by an oats bioassay. DCPA caused the least oat injury initially, and also after 13 weeks. None of the herbicides persisted in amounts toxic to oats for as long as 22 weeks when applied at concentrations approximately equivalent to field rates necessary for weed control. The residual toxicities of these same herbicides, after 22 weeks or longer, were also determined in Bosket silt loam collected from two depths in two preplanting subsurface and two preemergence surface field experiments by using oats, cotton and / or soybeans as bioassay indicators. Results from field applications at rates recommended for weed control in cotton confirmed that neither DCPA, diuron, norea, nor trifluralin persisted in amounts toxic to oats, soybeans, or cotton; however, prometryne residues were moderately toxic to oats and soybeans. Prometyrne residues from a 4 lb/A non-incorporated subsurface treatment were nearly twice as toxic to oats 25 weeks after application, as were residues from the same amount applied as a surface preemergence treatment.

Recrystallized 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine), 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine), and 2-methylmercapto-4-ethylamino-6-isopropylamino-s-triazine (ametryne) were adsorbed on filter paper, and exposed to ultraviolet light (253.7 millimicrons) or sunlight. All underwent photodecomposition, which was different under ultraviolet light and sunlight.

The herbicides 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), and 2-methoxy-3,6-dichlorobenzoic acid (dicamba) each labeled in the carboxyl position were sprayed on a pasture consisting of a mixture of silver beardgrass (Andropogon saccharoides Swartz.), little bluestem (A. scoparius Michx.), and dallisgrass (Paspalum dilatatum Poir.) and a sideoats grama (Bouteloua curtipendula [Michx.] Torr.) pasture over a 3-year period. Plant samples were harvested at intervals between 1 hr and 16 weeks after treatment and residues determined by radioassay. No important differences were found in the persistence of herbicides or of different formulations of the same herbicide. Rainfall was the most important factor influencing the persistence of the herbicides. The little bluestem-silver beardgrass-dallisgrass samples harvested 1 hr after treatment with the butoxyethyl ester of 2,4,5-T contained both this ester and the acid of 2,4,5-T. One week after treatment, the acid of 2,4,5-T and unknown metabolites were found but no ester.

Foxtail sophora is a widely distributed problematic weed in western Iranian dryland farming systems. Little information is available on seed germination and seedling emergence of this weed species in response to environmental and agronomic factors. This study was conducted to address this knowledge gap. Maximum seed germination (80%) occurred at 25 C and decreased at lower temperatures (<1% at 5 C) or under fluctuating temperature regimes. Light and pH did not have any substantial effect on seed germination. Foxtail sophora was tolerant to osmotic stress and moderately tolerant to sodium chloride. It was tolerant to salinity and drought stress during germination, which suggests that the population of this weed may increase in western farmlands of Iran. No seedlings emerged when seeds were buried at depths greater than 6 cm, which indicates that minimum- and no-till systems would increase seedling emergence of this species. Therefore, using sweep cultivators would be beneficial in management of foxtail sophora seedlings in the drylands of west of Iran.

Field pea cultivars often differ in weed competition. In several crop types branching has been cited as one of the characteristics conferring competition with weeds. The objective of this study was to determine the difference in weed competition among field pea cultivars differing in basal branching and other characteristics. Ten field pea cultivars with divergent basal branching ability were seeded at 50 plants m−2 under weedy and weed-free conditions to evaluate their competition with weeds. Branching did not differ greatly between cultivars and was not associated with the weed competiveness of the field pea cultivars. The forage pea cultivars, which were leafed and had longer vines, were much more competitive than the semi-leafless grain cultivars. As a result, the forage cultivars were better able to suppress weeds and maintain their yield under weed presence. However, the absolute seed yield of the forage pea cultivars was low, making them a poor choice for seed production. Vine length and the leafy characteristic may be important genetic characteristics associated with competition in field pea cultivars.

Field studies were conducted in 2016 and 2017 in Clinton, NC, to determine the interspecific and intraspecific interference of Palmer amaranth (Amaranthus palmeri S. Watson) or large crabgrass [Digitaria sanguinalis (L.) Scop.] in ‘Covington’ sweetpotato [Ipomoea batatas (L.) Lam.]. Amaranthus palmeri and D. sanguinalis were established 1 d after sweetpotato transplanting and maintained season-long at 0, 1, 2, 4, 8 and 0, 1, 2, 4, 16 plants m−1 of row in the presence and absence of sweetpotato, respectively. Predicted yield loss for sweetpotato was 35% to 76% for D. sanguinalis at 1 to 16 plants m−1 of row and 50% to 79% for A. palmeri at 1 to 8 plants m−1 of row. Weed dry biomass per meter of row increased linearly with increasing weed density. Individual dry biomass of A. palmeri and D. sanguinalis was not affected by weed density when grown in the presence of sweetpotato. When grown without sweetpotato, individual weed dry biomass decreased 71% and 62% from 1 to 4 plants m−1 row for A. palmeri and D. sanguinalis, respectively. Individual weed dry biomass was not affected above 4 plants m−1 row to the highest densities of 8 and 16 plants m−1 row for A. palmeri and D. sanguinalis, respectively.

In the midwestern United States, biotypes of giant ragweed resistant to multiple herbicide biochemical sites of action have been identified. Weeds with resistance to multiple herbicides reduce the utility of existing herbicides and necessitate the development of alternative weed control strategies. In two experiments in southeastern Minnesota, we determined the effect of six 3 yr crop-rotation systems containing corn, soybean, wheat, and alfalfa on giant ragweed seedbank depletion and emergence patterns. The six crop-rotation systems included continuous corn, soybean–corn–corn, corn–soybean–corn, soybean–wheat–corn, soybean–alfalfa–corn, and alfalfa–alfalfa–corn. The crop-rotation system had no effect on the amount of seedbank depletion when a zero-weed threshold was maintained, with an average of 96% of the giant ragweed seedbank being depleted within 2 yr. Seedbank depletion occurred primarily through seedling emergence in all crop-rotation systems. However, seedling emergence tended to account for more of the seedbank depletion in rotations containing only corn or soybean compared with rotations with wheat or alfalfa. Giant ragweed emerged early across all treatments, with on average 90% emergence occurring by June 4. Duration of emergence was slightly longer in established alfalfa compared with other cropping systems. These results indicate that corn and soybean rotations are more conducive to giant ragweed emergence than rotations including wheat and alfalfa, and that adopting a zero-weed threshold is a viable approach to depleting the weed seedbank in all crop-rotation systems.